Soft silicone elastomers are employed in technology, particularly as sealants. So-called plasticizers are used in these moisture-crosslinking silicone rubbers in order to reduce the crosslinking density and thus the hardness of the product. In principle, all unreactive substances are suitable for this if they are compatible with the silicone matrix. For example, .alpha.,.omega.-bis-(trimethylsiloxy)dimethyl-polysiloxanes are usually used as plasticizers in the 1-component sealants. Although chemically very similar polymers, which differ only by their terminal groups, are mixed during this, the nonfunctional silicone oils exude from the cured rubber when pressure is applied. This technical disadvantage is accepted normally as a necessary disadvantage in the sealant sector.
As is known from DE-A No. 1,769,537, the moduli at 100% elongation of the particular filler-containing, moisture-crosslinking silicone rubbers can be reduced by the use of mixed functional siloxanes (for example 14% of trimethylsiloxy and 86% of dimethoxy(methyl)siloxy terminal groups) in place of bifunctional siloxanes (100% of dimethoxy(methyl)siloxy terminal groups). The hardness of the product is not affected.
It was not known what influence such partly-functional oils have in filler-containing platinum-catalysed addition systems. Those skilled in the art would expect that it would be possible to transfer the disadvantageous effects described in DE-A No. 1,769,537 to the selectively crosslinked addition systems.